It is known to detect positive and negative ions by using a conversion anode to convert ions to secondary particles and then using a continuous dynode electron multiplier to provide a signal indicative of the abundance of ions. Stafford U.S. Pat. No. 4,423,324 discloses such a detector which may output a signal indicating the total of all positive and negative ions or may be multiplexed to produce a signal sequentially proportional to positive and then negative ions.
It is also known to provide microchannel plates with distinct electrode patterns such as distinct strips. In operation, the strips are sequentially activated to provide a sequential view of particle position.